U.S. patent application number 10/918149 was filed with the patent office on 2006-02-16 for mixed-color light emitting diode apparatus, and method for making same.
Invention is credited to Ken A. Nishimura.
Application Number | 20060033423 10/918149 |
Document ID | / |
Family ID | 35799354 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060033423 |
Kind Code |
A1 |
Nishimura; Ken A. |
February 16, 2006 |
Mixed-color light emitting diode apparatus, and method for making
same
Abstract
A mixed-color light emitting diode (LED) apparatus may be made
by forming a pixellated array of LEDs on a substrate, and then
placing phosphors over at least some of the LEDs. The phosphors are
chosen to convert light emitted by the LEDs to one or more
different colors. The LEDs may be lithographically printed on the
substrate, and the phosphors may be lithographically printed on the
LEDs.
Inventors: |
Nishimura; Ken A.; (Fremont,
CA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES, INC.;Legal Department, DL429
Intellectual Property Administration
P.O. Box 7599
Loveland
CO
80537-0599
US
|
Family ID: |
35799354 |
Appl. No.: |
10/918149 |
Filed: |
August 13, 2004 |
Current U.S.
Class: |
313/501 ;
257/E25.02 |
Current CPC
Class: |
H01L 25/0753 20130101;
H01L 2924/0002 20130101; G09F 13/20 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101; G09F 13/22 20130101 |
Class at
Publication: |
313/501 |
International
Class: |
H01J 1/62 20060101
H01J001/62 |
Claims
1. A mixed-color light emitting diode (LED) apparatus, comprising:
a substrate; a pixellated array of LEDs formed on the substrate;
and a plurality of phosphors placed over at least some of the LEDs,
said phosphors converting light emitted by the LEDs to one or more
different colors.
2. The apparatus of claim 1, wherein the pixellated array comprises
LEDs which are nominally identical in material composition and
color of light emission.
3. The apparatus of claim 1, wherein the LEDs are blue LEDs.
4. The apparatus of claim 3, wherein the phosphors convert light
emitted by some of the blue LEDs to one of two different
colors.
5. The apparatus of claim 3, wherein: wherein the phosphors convert
the light emitted by about twenty-five percent of the blue LEDs to
red light; and the phosphors convert the light emitted by about
fifty percent of the blue LEDs to green light.
6. The apparatus of claim 1, wherein the LEDs are near-ultraviolet
LEDs.
7. The apparatus of claim 6, wherein the phosphors convert light
emitted by some of the blue LEDs to one of three different
colors.
8. The apparatus of claim 6, wherein: the phosphors convert the
light emitted by about twenty-five percent of the near-ultraviolet
LEDs to red light; the phosphors convert the light emitted by about
fifty percent of the near-ultraviolet LEDs to green light; and the
phosphors convert the light emitted by about twenty-five percent of
the near-ultraviolet LEDs to blue light.
9. The apparatus of claim 1, wherein the LEDs are formed from InGaN
alloy.
10. The apparatus of claim 1, wherein the phosphors are
lithographically printed on the LEDs.
11. A method for making a mixed-color light emitting diode (LED)
apparatus, comprising: forming a pixellated array of LEDs on a
substrate; and placing phosphors over at least some of the LEDs,
said phosphors being chosen to convert light emitted by the LEDs to
one or more different colors.
12. The method of claim 11, wherein the LEDs are formed on the
substrate simultaneously, and are nominally formed of the same
material composition.
13. The method of claim 11, wherein the pixellated array is formed
by: depositing an LED layer structure on a substrate; and
selectively etching portions of one or more layers of the LED layer
structure, thereby forming the pixellated array of LEDs.
14. The method of claim 13, wherein the selective etch is performed
by photolithographically defining the areas to etch.
15. The method of claim 14, wherein the LEDs are blue LEDs.
16. The method of claim 15, further comprising, selecting and
printing phosphors that cause light emitted by some of the blue
LEDs to be converted to one of two different colors.
17. The method of claim 16, further comprising, printing phosphors
that convert blue light to green light on about fifty percent of
the blue LEDs, and printing phosphors that convert blue light to
red light on about twenty-five percent of the blue LEDs.
18. The method of claim 14, wherein the LEDs are near-ultraviolet
LEDs.
19. The method of claim 18, further comprising, selecting and
printing phosphors that cause light emitted by some of the
near-ultraviolet LEDs to be converted to one of three different
colors.
20. The method of claim 19, further comprising: printing phosphors
that convert near-ultraviolet light to red light on about
twenty-five percent of the near-ultraviolet LEDs; printing
phosphors that convert near-ultraviolet light to green light on
about fifty percent of the near-ultraviolet LEDs; and printing
phosphors that convert near-ultraviolet light to blue light on
about twenty-five percent of the near-ultraviolet LEDs.
Description
BACKGROUND
[0001] Direct view, mixed-color (e.g., red, green and blue (RGB))
displays are often formed using a combination of thin-film
transistor (TFT) and liquid crystal technologies. Another
alternative is to form a display using light emitting diodes
(LEDs). That is, a plurality of LEDs of different colors (e.g.,
RGB) may be arranged on a substrate in pixellated fashion. However,
the formation of displays using different colored LEDs has been
hampered by high manufacturing costs, as it is difficult to
properly place and attach millions of differently colored LEDs
(e.g., RGB) to a common substrate.
SUMMARY OF THE INVENTION
[0002] In one embodiment, a mixed-color light LED apparatus
comprises a substrate, a pixellated array of LEDs formed on the
substrate, and a plurality of phosphors placed over at least some
of the LEDs. The phosphors convert light emitted by the LEDs to one
or more different colors.
[0003] In another embodiment, a method for making a mixed-color LED
apparatus comprises 1) forming a pixellated array of LEDs on a
substrate, and placing phosphors over at least some of the LEDs
(with the phosphors being chosen to convert light emitted by the
LEDs to one or more different colors).
[0004] Other embodiments are also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Illustrative and presently preferred embodiments of the
invention are illustrated in the drawings, in which:
[0006] FIG. 1 provides a plan view of an exemplary mixed-color LED
apparatus;
[0007] FIG. 2 provides a cross-sectional view of the LED apparatus
shown in FIG. 1;
[0008] FIG. 3 illustrates a method for making a mixed-color LED
apparatus such as that which is shown in FIGS. 1 & 2; and
[0009] FIGS. 4-10 illustrate the making of a mixed-color LED
apparatus using an exemplary embodiment of the FIG. 3 method.
DETAILED DESCRIPTION OF THE INVENTION
[0010] One reason for the lower manufacturing cost of a TFT/LCD
display (versus an LED display) is that the electrical and
colorizing components of a TFT/LCD display are separately
manufactured, and then mated together. That is, the TFTs of a
TFT/LCD display are formed on a first substrate (typically
silicon), and the color filters of a TFT/LCD display are formed on
a second substrate (typically glass). The two substrates are then
aligned and mated with other display components in a sandwich-like
assembly process. Often, the display's TFTs are formed on a
substrate using a lithographic printing process.
[0011] In contrast to a TFT/LCD display, the electrical and
colorizing components of an LED display are integrated. That is,
the material used to manufacture an LED (an electrical element)
determines the color of light that will be emitted from the LED.
Hence, the color of light that is emitted from an LED is fixed.
This also fixes the color of light that is emitted from a given
position in an LED display. Thus, in an RGB LED display, a
pixellated array of red, green and blue LEDs, each of which is
formed using a different type of material, needs to be formed on a
common substrate. This co-manufacture of different types of devices
on a common substrate has made the manufacture of LED displays
difficult.
[0012] FIGS. 1 & 2 illustrate a mixed-color LED apparatus 100,
wherein a pixellated array of LEDs 104-134 are formed 302 (FIG. 3)
on a substrate 102 (e.g., a wafer or die of material such as
silicon). A plurality of phosphors 136-158 are then placed 304 over
at least some of the LEDs 104-118, 128-134, such that the phosphors
136-158 convert light emitted by the LEDs 104-18, 128-134 to one or
more different colors.
[0013] By way of example, the LEDs 104-134 of the apparatus 100 may
be nominally identical in material composition and color of light
emission and, by way of example, may be blue or near-ultraviolet
LEDs. As known in the art, these types of LEDs may be formed using
an Indium-Gallium-Nitride (InGaN) alloy.
[0014] The pixellated array of LEDs 104-134 may be formed by
depositing an LED layer structure on the substrate 102. In one
embodiment, the LED layer structure comprises a number of active
semiconductor layers sandwiched between upper and lower
metallization layers. By way of example, the LED layer structure
may be formed by first depositing a metal layer 400 (e.g., a
thickfilm; see FIG. 4) on the substrate 102. This layer 400 may
then be photolithographically patterned and etched to form
individual and/or interconnected electrical contacts; or, as shown,
this layer could be used as a node or terminal that is common to
all LEDs 104-134. The requisite layer(s) 500 needed to form blue or
near-ultraviolet LEDs 104-134 are then deposited (see FIG. 5). In
one embodiment, these layer(s) 500 are grown using vapor
deposition. These layer(s) 500 may then be photolithographically
patterned and etched to form an array of active LED areas 104, 112,
120, 128 (see FIG. 6). At this stage of manufacture, each of the
active LED areas 104, 112, 120, 128 is surrounded by a perimeter
"void". These voids may optionally be filled with oxide 700, 702,
704 (FIG. 7) to present a planar surface over which a second metal
layer 800 (FIG. 8) may be deposited. This second metal layer 800
may then be photolithographically patterned and etched to form
contacts 900, 902, 904, 906 for individual ones and/or groups of
the active LED areas 104, 112, 120, 128 (see FIG. 9).
[0015] Depending on the number and types of layers in the LED layer
structure, its layers may be patterned and etched individually, or
at the same time.
[0016] Patterning and etching LEDs in accordance with the method is
not only more cost-effective than placing and attaching individual
LEDs on a substrate, it also provides for better alignment of the
LEDs.
[0017] Phosphors 136-158 that are capable of converting blue or
near-ultraviolet light to different colors of light (e.g., red,
green and possibly blue light) may then be placed over some or all
of the LEDs 104-118, 128-134 by, for example, lithographically
printing them on the LEDs (see FIG. 10). In this manner, an RGB
display (FIGS. 1, 2 & 10) may be formed using an array of only
blue or near-ultraviolet LEDs 104-134.
[0018] In one embodiment, phosphors 136-150 that convert blue light
to green light are printed on about fifty percent (50%) of the
display's LEDs 112-118, 128-134; and phosphors 152-158 that convert
blue light to red light are printed on about twenty-five percent
(25%) of the display's LEDs 104-110. In another embodiment,
phosphors that convert near-ultraviolet light to red light are
printed on about twenty-five percent (25%) of the display's LEDs;
phosphors that convert near-ultraviolet light to green light are
printed on about fifty percent (50%) of the display's LEDs; and
phosphors that convert near-ultraviolet light to red light are
printed on about twenty-five percent (25%) of the display's LEDs.
In these embodiments, each pixel in the display would comprise four
LEDs (e.g., 104, 112, 120, 128), the colors of which would be mixed
(e.g., by regulating the drive currents of the LEDs) to produce the
color of a single image pixel.
[0019] Although examples have been provided wherein only blue or
near-ultraviolet LEDs are formed on a substrate, other colors of
LEDs (e.g., red or green) could also be formed on a substrate.
Further, more than one type of phosphor could be placed over some
or all of the LEDs. For example, a mix of phosphors that emit light
in red, green and blue wavelengths could be placed over an LED to
generate a white light.
[0020] It is also envisioned that apparatus formed in accordance
with some or all of the above teachings need not be a full-color
display. That is, any form of mixed-color LED apparatus (i.e., a
display wherein two or more colors of light are mixed to produce
the color of an image pixel) may be formed using the above
teachings. One could also form a merely utilitarian or decorative
device using the above teachings. Exemplary utilitarian devices
include lamps and other light sources, or display backlights. An
exemplary decorative device would be mood lighting.
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